/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function (n) {
  const dp = [0, 1, 2];
  if (n <= 2) return dp[n];
  for (let i = 3; i <= n; i++) dp[i] = dp[i - 1] + dp[i - 2];
  return dp[n];
};
